Active defensive role

The role of antiproliferative effects of an activated defense reducing the next generation of herbivores compared with the straightforward action of toxins or feeding deterrent metabolites in the evolutionary arms race is still under discussion. The proposed mechanism suggests natural selection at the group level,... 

A re-examination of the defensive chemistry of I marginata revealed that the tridentatols (85-88) represent the transformation products of less active sulfate ester storage forms (81-84) [161]. Crushing the tissue as an attacking predator would do results in the rapid conversion of the sulfate esters within seconds after wounding. This suggests that this reaction plays a role in a wound-activated defense. 

Van Alstyne KL, Wolfe GV, Freidenburg TL, Neill A, Hicken C (2001b) Activated defense systems in marine macroalgae evidence for an ecological role for DMSP cleavage. Mar Ecol Prog Ser 213 53-65... 

PPO catalyses the dependent oxidation of phenolics to quinones. The secondary reactions of quinones lead to the formation of polymeric brown or black pigments, which are responsible for significant post-harvest losses of fruits and vegetables [72]. Finally, induced PPO activity consists of both systemic and localized components. Systemic induction of PPO in tissues in response to all types of injuries may represent a broad, defensive role for PPO in protection of juvenile tissues from subsequent attack by a broad spectrum of pathogens and pests [71]. 

The key enzymes of the system are the cytochrome P-450 enzymes, which have active sites that contain an iron atom that cycles between the +2 and +3 oxidation states. These enzymes bind to the substrate and molecular 02as part of the substrate oxidation process. Cytochrome P-450 is found most abundantly in the livers of vertebrates, reflecting the liver s role as the body s primary defender against systemic poisons. Cytochrome P-450 occurs in many other parts of the body, such as the kidney, ovaries, testes, and blood. The presence of this enzyme in the lungs, skin, and gastrointestinal tract may reflect their defensive roles against toxicants. 

The most prominent source of marine polypropionates are mollusks, in particular opisthobranchs (13). Among a variety of polypropionates, the simplest one is possibly siphonarienal (9) isolated from Siphonaria grisea, whereas such unusual pyrone-containing metabolites as siphonarin A (10) were isolated from S. zelandica. Marine polypropionates not only play defensive roles in mollusks, but also they show antimicrobial, anti vial, and cytotoxic activities. 

Studies have demonstrated that 1 plays a vital defensive role in plants. It has been shown that 1 possesses modest in vitro antimicrobial properties [2,7]. In addition, several oligomeric metabolites of 1 are known to exhibit greater antimicrobial activity [8]. Further evidence for the important defensive role of 1 in plants comes from studies in which transgenic barley, wheat, and tobacco plants containing a stilbene synthase gene exhibit enhanced resistance to fungal infection [9,10],... 

Several examples of physiologically-active compounds have been mentioned in passing—especially the cyanogenic glycosides whose major defensive role may be to protect seedlings from slugs and snails and the antibiotics from marine isonitriles. Unfortunately, the toxicity of the latter class precludes their adoption in medicine. 

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